Disinfectants can be defined as chemical agents that kill pathogenic organisms on inanimate objects. Disinfection is directed against viruses, bacteria and eukaryotic parasites, such as Giardia. Traditional disinfectants act in dilute solution by diverse mechanisms to kill microorganisms. When applied to drinking water, traditional disinfectants are undesirable because they generally leave rather high residual concentrations of the disinfectant in the water. Typical disinfectants include chlorine gas, aqueous iodine, aqueous silver nitrate, hydrogen peroxide, phenol, ethanol, and benzalkonium chloride.
Solid phase disinfectants are available that require that the pathogenic microorganisms contact a biocidal surface. Some of these disinfectants act without any measurable release of a chemical agent and are known as "contact disinfectants". Others contain traditional disinfecting agents in slow release formulations and are known as "constant release disinfectants". Finally, some solid phase disinfectants release a toxic dose of disinfectant to microorganisms upon contact, leaving very little residual disinfectant in the solution in the absence of any microorganisms and are called "demand release disinfectants".
Well known demand release type disinfectants include polyiodide resins. Polyiodide resins inactivate a wide variety of microorganisms including Giardia cysts leaving a very small residual amount of iodine in the treated solution. These types of resins are very stable and have been used in portable water purifiers, home water purifiers, and by the U.S. Space Program. G. L. Marchin et al., "Contact and Demand Release Disinfectants" in C.R.C. Critical Reviews in Environmental Control, 19:227 (1989).
Known methods for preparing polyiodide resins are not readily adapted to industrial scale production. For example, batch methods involving stirring the resin beads for 24 hours with a solution of I.sub.3.sup.- are described in U.S. Pat. Nos. 3,817,860 and 3,923,665. The I.sub.3.sup.- solution is formed by mixing elemental iodine with potassium iodide. These batch methods are not suitable for industrial use because of the difficulty of mixing large scale amounts of elemental iodine with potassium iodide without causing iodine recrystallization and because they require excessive amounts of reagents. Improper preparation of resin in this manner can produce a high polyiodide residual in the treated effluent and result in incrustation of elemental iodine within the resin bed.
A method for producing polyiodide resins using a fluidized bed system is described in U.S. Pat. No. 4,238,477. In this method, water free of halide ions is used as a carrier to apply elemental iodine gradually and uniformly to the resin. However, this process would require a very large expenditure on capital equipment, and would be quite expensive to operate. First of all, to obtain processing times which are less than several days running time, temperatures close to the boiling point of the water solution are required. Consequently, pressure vessels are required which could handle the large pressures which would develop should the temperature go a bit too high. In addition, corrosion resistant materials such as glass and Teflon are required to offset the caustic effects of the hot iodine solution. Such elevated temperatures will also cause a partial pressure of I.sub.2 vapor, which is potentially hazardous. As a result, the cost of capital equipment involved in such a process would be prohibitively large. Furthermore, heating and maintaining a constant temperature throughout the system to avoid precipitation of iodine on any of the surfaces contacted by the solution for such long processing times would be extremely expensive in a large-scale system.
Thus, there is a need to develop a method for producing a polyhalide resin disinfectant that is less prone to safety-related problems, is more cost efficient, and is easier to manufacture on an industrial scale.